This invention relates to the illumination of a visual display terminal and its surroundings. More specifically, the invention concerns the illumination of the keyboard, sides, back, and the area above a visual display terminal.
Prior to this invention, visual display terminals have been illuminated with luminaires fixedly mounted on the ceiling above the terminal or on a wall or partition above and behind the display terminal. Also, there has been developed an illumination system whereby a luminaire mounted above the terminal is horizontally adjustable toward or away from the operator of the terminal to vary the illumination of the keyboard and face of the display terminal.
This prior art scheme has not been completely successful in a number of respects. For example, it has been found deficient in that, as the luminaire is moved forward toward the operator, the wall or backpanel behind the terminal darkens and an objectionable brightness contrast develops between the areas illuminated by the luminaire and the wall or backpanel. An objectionable contrast between the screen of the visual display terminal and the aforementioned wall or backpanel also develops. Another problem discovered is that the prior art luminaires tended to illuminate the person of the operator as the luminaire was moved toward the operator. The operator would see a reflection of his person in the screen of the visual display terminal which would veil the letters or numbers displayed thereon and thereby result in poor contrast and visibility. This problem is particularly troublesome when the operator wears light-colored clothing.
This invention overcomes the problem of brightness contrasts by providing a means for developing a separate backlighting component of illumination. More specifically, a visual display terminal luminaire is provided which directs a portion of the light output of the luminaire to the wall or backpanel behind the display terminal.
In one embodiment of this invention, a reflector is mounted in a luminaire which contains two light sources, preferably cylindrical lighting tubes, one of the light sources providing both illumination of the front, sides, and areas above the terminal, and the other of said sources providing both uplighting and backlighting. These light sources are fixed with respect to each other and are horizontally adjustable toward and away from the operator. The sources are mounted above the terminal, and their longitudinal axes are perpendicular to the direction in which the operator views the terminal.
In another embodiment of the invention, a shaped backlight reflector can preferably be provided in the above-described arrangement to selectively illuminate a portion of the wall or backpanel to reduce excessive brightness perceived by a person standing behind or to the sides of the visual display terminal. A further embodiment of the invention involves fixing of the above-mentioned light source which provides uplighting and backlighting adjacent to the backpanel and allowing only the light source which provides illumination of the front and sides of the terminal to be adjustable horizontally.
The invention overcomes the problem of veiling reflections on the screen of the visual display terminal by the provision of a vertically adjustable shield which is attached to the front fascia of the luminaire. In one embodiment the shield is slidably mounted on the fascia and in another embodiment it is hingedly mounted on said fascia.